1. Field of the Invention
The present invention relates to measurement techniques and in particular to a process monitoring system, a process monitoring method, and a method for manufacturing a semiconductor device.
2. Description of the Related Art
In semiconductor manufacturing process, a depth of an etched groove and a thickness of a deposited membrane are controlled by monitoring an etching time and a deposition time. However, such monitoring method cannot operate precisely when a process environment, such as temperature and pressure, is changed unexpectedly. The imprecise monitoring decreases the yield rate of the manufactured semiconductor devices. Therefore, process monitoring systems measuring the actual depth of the etched groove or the actual thickness of the deposited membrane has been recently introduced.
In Japanese Patent Laid-Open Publication No. 2002-93870, a process monitoring system is disclosed, in which an inspection light is irradiated on an object to be processed. The object is held in a process chamber. The light is irradiated through a monitor window provided in the process monitor. The disclosed system estimates the actual depth of the etched groove or the actual thickness of the deposited membrane on the object to be processed by detecting the reflected inspection light.
However, if the monitor window is composed of birefringent material and the inspection light is polarized, the monitor window interacts with the inspection light and modulates the phase of the light. Such phenomenon causes interference noises in a spectrum of the inspection light. Therefore, it is difficult to achieve a precise monitoring.
Also, an upper electrode is provided in the process chamber of plasma process. A plurality of nozzle holes is formed in the upper electrode in order to supply an interior of the process chamber with a reaction gas. However, if the monitor window is provided on the upper electrode, the monitor window disturbs a stable supply of the reaction gas since the monitor window does not include the nozzle holes. Therefore, the reaction gas concentration beneath the monitor window becomes less than in other space. Consequently, the evenness of an etching rate or deposition rate in the process chamber is decreased.